Present television receivers, such as NTSC (National Television Standards Committee) television receivers, include video processing circuitry that typically must process a video signal conforming to only a single, predetermined video format. Future digital television (DTV) receivers are expected to be implemented substantially in accordance with the transmission standards established by the Advanced Television Standards Committee (ATSC). A similar standard is the European Digital Video Broadcasting (DVB) standard. The ATSC and DVB standards are incorporated herein by reference in their entireties.
A compressed digital video system is described in the ATSC digital television standard document A/53, incorporated herein by reference. Moreover, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1, refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is incorporated herein by reference. The new DTV standards allow broadcasters to deliver virtually any format up to 1920xc3x971080 pixels. Specifically, DTV receivers must be capable of receiving source video comprising image sequences that vary in spatial resolution (480 lines, 720 lines, or 1080 lines), in temporal resolution (60 fps, 30 fps, or 24 fps), and in scanning format (2:1 interlaced or progressive scan).
It is known in the computer industry to display multiple graphics formats on a so-called xe2x80x9cmultisyncxe2x80x9d display device. Specifically, a multisync display changes horizontal and/or vertical scanning frequencies in response to a change in graphics format. Such a multisync approach may be implemented in a video or television environment by using, e.g., studio equipment raster formats standardized by the Society of Motion Picture and Television Engineers (SMPTE). Unfortunately, the multisync approach leads to an increase in cost due to the more complicated deflection circuitry, an increase in power consumption, and a high inter-format switching latency (i.e., greater than one video frame) due to long time constants associated with deflection coil inductance.
A better approach was disclosed by Lee in U.S. Pat. No. 5,485,216, issued Jan. 16, 1996 for Video Conversion Apparatus for High Definition Television, incorporated herein by reference in its entirety. In the Lee patent, a high definition television signal is decoded, then converted to a 30 Hz frame rate, then vertically decimated, then horizontally decimated and then interleaved to produce a 30 Hz, 1050 vertical scanning line video signal. Thus, the Lee arrangement provides a brute force technique for converting a high definition television signal into a 30 Hz, 1050 vertical scanning line video signal. The format-converted television signal is then processed in a conventional manner to produce a picture.
Unfortunately, the Lee arrangement disadvantageously requires complex timing, switching and video processing circuitry. In addition, the television signal produced by the Lee arrangement will inherently cause motion video artifacts on a display device in the case of 24 Hz source video (e.g., such as film). This is because the Lee arrangement uses the well known 3:2 pull-up sequence to convert 24 frames per second video into 60 frames per second, which results in motion jitter artifacts when the converted video is displayed. Since most prime time television is mastered on film, a large percentage of video material will be continue to be transmitted in one of the 24 Hz progressive scan formats.
Therefore, a need exists in the art for a cost-effective video processing system suitable for use in, e.g., a multiple format television receiver. It is also seen to be desirable to provide a video processing system that adapts to use of 24 Hz source video.
The invention is a method and concomitant apparatus for electronic format and frame rate conversion in a multiple format video processing system adapted to avoid display motion artifacts causes by 3:2 conversion of 24 Hz video source video by tripling the frame rate of the source video and responsively adjusting the format of the resultant video signal.
The invention preserves at least a multiple of the frame rate of a display device by adapting the spatial resolution of a digital video signal to be presented on the display device. The transmitted display format (i.e., horizontal and/or vertical resolution of the transmitted picture) is adapted to be compatible with an integer multiple of the transmitted picture frame rate.
One embodiment of the invention comprises an apparatus for processing a digital video signal including video imagery associated with at least one of a plurality of transmitted display formats to produce an output video signal suitable for presentation on a display device, the display device having associated with it a single predetermined horizontal scanning frequency, the apparatus comprises: a horizontal resizer, for adapting a horizontal format of the digital video signal in response to a first control signal; a vertical resizer, for adapting a vertical format of the digital video signal in response to a second control signal; a frame rate converter, for adapting by an integer multiple a frame rate of the digital video signal in response to a third control signal; and a controller, for generating the first, second and third control signals in response to the transmitted display format of the video imagery included within the digital video signal; wherein the controller causing the horizontal resizer to adapt the horizontal format of the digital video signal to a size compatible with the predetermined horizontal scanning frequency of the display device; the controller causing the vertical resizer to adapt the vertical format of the digital video signal to a size compatible with the adapted horizontal format of the digital video signal; and the controller, in the case of an input video signal having a frame rate of 24 Hz or 25 Hz, causing the frame rate converter to double, triple or quadruple the frame rate of the digital video signal.